The House on the isle of Ely was a large structure that possessed an artificial intelligence. Drawing its power from the Moon and stars, it could recognise what the occupants of the House truly desired. Using a technological form of telepathy, the House could "grant wishes" even before the residents could realise what they want.
Because of this, the newlywed couple that lived in the House could have anything they wanted. But the wife had a thought about the husband and the House subsequently killed him to fulfil her wish. She then wished herself dead. The House then stopped all the molecules within, essentially freezing time within the House.
The First Doctor, Steven Taylor, and Sara Kingdom visited the House. While Sara wanted to know what had happened, the Doctor and Steven wanted to leave, but her thoughts made the House take Steven away and trap the Doctor and the TARDIS within glass boxes. Trying to escape, Sara made contact with a touch panel and gave a copy of her mind for the House's intelligence to use, allowing it to make more moral judgments and understand the consequences of its actions instead of just reacting to the thoughts of the moment.
Over a thousand years, the House changed its form to suit the people who stayed. The copy of Sara used her judgement to cast people out of the House or let them stay. She also wondered if other Houses existed. (AUDIO: Home Truths)